Hard surface coated gear member



May 27, 1958 A. MNSTER ETAL 2,836,514

HARD SURFACE COATED GEAR MEMBER Filed Nov. 15. 1954 Unite Stats ant HARDSURFASE @DATED GEAR NEMBER Arnold Mnster and Richard Weber, Frankfurt amMain,

Germany, assignors to Metailgesellschaft Aktiengeseilschaft, Frankfurtam Main, Germany, a corporation o Germany Cil Gear Wheels, such as spurgears, bevel gears, pinions, worms and worm wheels for heavy duty, andsprockets are subjected to particularly high stresses because thesupporting areas of the flanks are very small and the build-up of alubricating film is impaired by the pressures prevailing. For thisreason the wear at the ilanks is very high and it is endeavored toprovide a high Wear resistance of the mating surfaces by a properselection of the material and design and to separate the matingsurfaces,

e. g., by the use of special lubricants.

It has been found that a substantial improvement in the wear resistanceof the tooth iianks can be achieved by providing at least these mosthighly stressed parts of the gear wheels with a coating of a hardnitride, hard boride and/or hard silicide of the metals of groups 3 to 6of the periodic system, which coating may contain also hard carbides ofmetals of groups 3 to 6 of the periodic system, preferably in ahomogeneous form, as mixed crystals with the other hard substances, orin a heterogeneous form. The hard compounds may be applied as mixedlayers, e. g. of mixed crystals, or in separate layers. Such layers maybe applied on the steels preferred for gear Wheels, as well as on othermaterials, such as bronzes. The wearing qualities of the base materialused are not critical because the coating applied according to theinvention has a very high wear resistance and possesses the strength andcoherence necessary to resist impacts.

The coating is preferably applied out of the gaseous phase.

Coatings of titanium nitride may be precipitated directly on the surfaceof the workpiece, e. g., by the following reaction:

Suitable hard nitrides include in addition to titanium nitride thenitrides of zirconium, hafnium, vanadium, columbium and tantalum.

To produce coatings consisting of silicides the metal which is to formthe silicide may be precipitated rst on the surface to be coated, e. g.,according to the following reaction:

l2,836,531: Patented May 27, 1958 Then the metal may be converted to itssilicide by a known method, e. g., according to the following reaction:

Ti+SC1i1+2H2=titanium silicide-l-4HC1 (3) mixed-crystal coating oftantalum carbide and tantalumv nitride may be produced by precipitatingtantalum from a mixture of hydrogen and tantalum pentachloride vapor,and transforming said tantalum to a mixture of tantalum carbide andtantalum nitride by annealing in a mixture of nitrogen and hydrocarbons.Thus a hard coating is obtained which is able to follow a deformation ofthe ground material.

A heterogeneous coating consisting of a layer of titanium nitride and alayer of titanium carbide may be applied by coating the workpiece withtitanium nitride rst, according to Reaction l. By reacting a gas mixtureconsisting of titanium tetrachloride, hydrogen, and hydrocarbons such asmethane, another layer consisting of titanium carbide is precipitated onsaid titanium nitride layer.

The drawing shows a gear wheel 1 the teeth of which have a coating 2 oftitanium nitride.

What is claimed is:

l. A gear member having a hard coating on its mating surface portionsconsisting of a coating comprising at least one compound selected fromthe group consisting of titanium nitride, titanium silicide and titaniumboride deposited by a gas phase reaction.

2. A gear member having a hard coating on its mating surface portionsconsisting of a coating comprising titanium nitride deposited by a gasphase reaction.

3. A steel gear member having a hard coating on its v mating surfaceportions consisting of a coating comprising titanium nitride depositedby a gas phase reaction.

4. A bronze gear member having a hard coating on its mating surfaceportions consisting of a coating comprising titanium nitride depositedby a gas phase reaction.

References Cited in the le of this patent UNITED STATES PATENTS1,098,794 Fleming June 2, 1914 1,794,810 Van Arkel et al. Mar. 3, 19311,923,814 Egan Aug. 22, 1933 2,307,005 Ruben Dec. 29, 1942 2,331,909Hensel et al. Oct. 19, 1943

1. A GEAR MEMBER HAVING A HARD COATING ON ITS MATING SURFACE PORTIONSCONSISTING OF A COATING COMPRISING AT LEAST ONE COMPOUND SELECTED FROMTHE GROUP CONSISTING OF TITANIUM NITRIDE, TITANIUM SILICIDE AND TITANIUMBORIDE DEPOSITED BY A GAS PHASE REACTION.